The invention relates to the inspection of bearing balls. In the manufacture of bearing balls such as in the aerospace and aircraft industry, an assessment of the condition and appearance of the ball is required for reliable operation. In many applications of the bearing balls, such as in the main shaft of an aeroengine, defects and faults in the bearing ball may lead to premature failure of the bearing and subsequent damage or destruction.
The accurate inspection of the entire bearing surface of the ball is a problem which has given the manufacturer considerable trouble. Due to the minute nature of the possible defects including overheating cracks, unequal distribution of carbon, marks from oxidation, corrosion pitting and hard impact marks, and indentations the problem is compounded. The small size of the bearing ball necessitates accurate control of the inspection process in order to insure that the entire surface of the bearing ball is inspected.
In one prior method, an automatic feed mechanism passes balls through a cleaning tank into an oil immersion tank where they are picked up by an electric drive mechanism. While being continuously rotated, the balls are subjected to ultra sound which both refracts at the surface of the ball and propagates into the ball. If the wave meets a flaw, it is reflected back along its path, detected, displayed on a cathode ray tube and recorded on an ultraviolet chart. However, this technique requires immersion of the ball, probe, and an elaborate ball positioning mechanism in a fluid tank and is limited to larger ball diameters. Because of the requirement of a fluid couplant, periodic attendant cleaning of the equipment is required. Very sophisticated, and costly equipment is thus required. The complexity of the equipment subjects the inspection process to unreliability.
In another prior technique, three independently driven rollers were utilized to roll the bearing ball while in the proximity of a probe. A separate motor drive was required for each of the rollers which are then driven in a manner which would most likely assure inspection coverage of the ball. However, in order to control the ball movement elaborate control of the roller motors was required.